This proposal describes a comprehensive training program to transition Dr. de Zoeten from a mentored scientist into an independent investigator in the area of Pediatric Gl and Hepatology. He will focus on the study of the immunopathology of inflammatory bowel disease (IBD), with the ultimate purpose of ameliorating this and other complex intestinal disorders. Over the course of these studies, the PI will acquire laboratory skills, research training, and critical reagents which will enable him to begin work as an independent physician/scientist. Inflammatory bowel disease (IBD) involves dysregulation of mucosal T cells. There is currently much interest in the functions of naturally occurring CD4+CD25+ regulatory T cells (Tregs) - distinguished from other CD4+ cells by baseline expression of CD25 and intracellular expression of FoxpS - as agents to regulate inflammation. Histone deacetylases (HDACs) are enzymes that deacetylate lysine residues and induce transcriptional repression through chromatin condensation. When HDACs are inhibited, lysine residues on histone tails become hyperacetylated, chromatin becomes accessible for transcription factor binding and gene transcription occurs. It is now also recognized that non-chromatin proteins can be regulated by acetylation and de-acetylation. Histone deacetylase inhibitors (HDACi) typically bind the catalytic sites of HDACs, blocking substrate access, thereby allowing histone acetylation and gene transcription. While HDACi are mainly being evaluated as anti-cancer agents, they have also been evaluated in models of inflammation. We plan to utilize these compounds in the treatment of IBD. The proposed studies will assess the effects of HDACi, including Trichostatin A (TsA), Suberolylanilide hyroxamic acid (SAHA) and/or valproate in 3 different models of colitis. We will also use these models to determine which HDACs are involved in colitis, and whether Tregs are critical to the beneficial effects of HDACi on colitis. We have noted that treatment of mice with TsA is associated with FoxpS acetylation and we will therefore evaluate, through mutagenesis of key lysines on Foxp3, if the effects of HDACi is dependent upon acetylation of those sites. Finally, we note multiple HDACs are elevated in activated Tregs and plan to examine the relative importance of these HDACs so as to assess whether future selective HDACi therapy may be warranted. Relevance: The information which will be obtained from this and future investigations will improve our understanding of the immunopathology of IBD, as well as the epigenetic regulation of regulatory T cells, and may enhance the therapy and prevent complications of this disease.